For many years, rotary retort furnaces have been used in the heat treatment, e.g., carburizing, carbo-nitriding, carbon restoration, or hardening of a variety of workpieces, such as screws, nuts, bolts, washers, rivets, pins, balls and springs. Many of the retorts used in these furnaces are provided with an internal helical flight or spiral adapted to transport the workpieces through the retorts as they rotate in the furnace.
In the past, it has been common practice to provide a retort with a pair of bell-shaped ends which may be used as bearing-engaging supports for the retort when the ends are disposed externally of a furnace (see, for example, Sheahan U.S. Pat. No. 3,556,498). Workpieces which have been transported through the retort are discharged through openings provided in the circumferential surface of the retort near one end thereof. Because the number and size of the discharge openings which may be provided in the circumferential surface of the retort are limited, it is difficult to achieve a uniform rate of discharge. Also, the bell-shaped ends are difficult and, therefore, expensive to form, for instance, by casting.
Rotary retorts which have wide-mouth open ends, as compared with bell-shaped ends, can discharge workpieces directly from an end thereof, rather than through discharge openings in the circumferential surface of the retort, and, thus, avoid the two problems or disadvantages discussed above which plague the known retorts having bell-shaped ends. However, problems are encountered in supporting the discharge ends of such retorts for rotation in a furnace. For instance, because the discharge end should be located within the furnace to provide improved quenching of the discharged workpieces, it is impractical to provide an entire support assembly, including a bearing or roller, inside the furnace, due to the adverse affect that the furnace atmosphere would have on the operating life of the bearing or roller.
Open-ended rotary retorts have been developed which are adapted for support externally of a furnace. For instance, Smith et al. U.S. Pat. Nos. 4,025,297 and 4,069,007 disclose a rotary retort furnace in which a retort is supported for rotation at only one end outside of the furnace, so that the retort is cantilevered into the furnace. The cantilevered retort of the Smith et al. patents is, however, subject to droop and fatigue and, therefore, undesirable.
In Heyer et al. U.S. Pat. No. 3,441,257 and Mesher et al. U.S. Pat. No. 3,927,959, there is disclosed a heat treating furnace having a cylindrical open-ended retort mounted for rotation therein. The discharge end of the retort is provided with a cone-shaped apron, one end of which abuts against the discharge end of the retort. The other end of the apron protrudes radially through the furnace where it, and hence the discharge end of the retort, is rotatably supported by a plurality of rollers. Such a support assembly for the discharge end of the retort is undesirable because it requires the use of a special sealing and cooling means which is subject to rapid wear and requires frequent lubrication and adjustment. In addition, the apron, which serves as both an atmosphere seal and a support, is subject to warping and cracking, thereby impairing the integrity of the atmosphere seal and, simultaneously, the smoothness of rotation of the retort. Furthermore, workpieces exiting from the discharge end of the retort are discharged through a relatively cold chute, as a result of the chute being isolated from the heating chamber of the furnace by the apron. Because the workpieces are discharged through a relatively cold chute before they enter a suitable quench media, the workpieces are subjected to a chilling effect which is deleterious to proper hardening prior to quenching.
In order to improve upon the apron and seal arrangement disclosed in the Heyer et al. and Mescher et al. patents, the assignee of the present application developed a heat treating furnace, described and illustrated in Shaefer et al. U.S. Pat. No. 3,836,324, having a rotary retort equipped with a circumferential collar which protrudes radially through the furnace intermediate the ends thereof and provides an enlarged heated discharge chamber from which the workpieces can be dropped directly into a quench media without the chilling effect which is produced by the retort of the Heyer et al. and Mescher et al. patents. Despite the substantial advantages of the collar and support assembly described and illustrated in the Shaefer et al. patent, the retort still suffers from some of the same problems and disadvantages as those summarized above in the foregoing discussion of the Heyer et al. and Mescher et al. patents.